This invention relates to a magnetic tape cassette, and more specifically to a cassette with a pressure pad of an improved design.
Ordinary magnetic tape cassettes have a pressure pad as shown in FIG. 1, comprising a leaf spring 1 and a pad piece 2 to press the magnetic tape against the tape head for magnetic recording or playback. Extending the description to FIGS. 3 and 4, the conventional pressure pad consists of a pad piece 2 of felt or the like mounted on the middle portion of a leaf spring 1 which is an elastic metal strip of phosphor bronze or the like bent at both ends to a wide U shape. The entire back side of the pad piece 2 is supported by an enlarged portion of the spring 1, but the force with which the spring urges the magnetized side of the tape against the head is not even, and hence the sensitivity of signal recording and reproduction is not uniform. To be more exact, the pressure of contact with the head that the pad 2 is caused to exert on the magnetic tape 3 running in the direction of the arrow while being pressed against the head is not even across the tape. This will be explained in further detail with reference to FIGS. 2 and 5. In operation of a recorder the magnetic head 4 enters the cassette at its opening into contact with the pressure pad through the magnetic tape 3. As shown in FIG. 5, when the leaf spring 1 forces the magnetic tape 3 against the face 5 of the magnetic head, the tape 3 is subjected to a pressure distributed as indicated by the arrows of varying lengths. Accordingly, the contact pressure of the magnetic tape applicable to magnetic cores 6a, 6b (for left and right channels) set in the side of the magnetic head 4 facing the tape is not uniform; the contact pressure of the tape being exerted on the core 6b is less than that on the core 6a. The recording-reproducing sensitivity of the magnetic tape through the left-channel core 6b is consequently lower. This point will be further clarified later by a comparative description of the present invention. The low contact pressure of the magnetic tape with the left-channel core of the head poses another problem, i.e., wide variation in the recording-reproducing sensitivity. This, too, will be made clear later.